Continuous method of manufacturing ablative and refractory materials



Dec. 27, 1966 M. TURKAT 3,

CONTINUOUS METHOD OF MANUFACTURING ABLATIVE AND REFRACTORY MATERIALSFiled April 21, 1964 FIG. I. FIG, 2. VACUUM 3! FURNACE TO EXHAUST GAS I,33 ilgiKl NG ,/DE POSITION LAYER TOP FLAT SURFACE 22 .5 LIFTER go 38FILAMENT COMING OFF GROOVE LIFTER SHAPED FILAMENTS COMING OFF FIG. 3,FIG, 3A,, METHANE 3 (3 ARGON HYDROGEN l V Q a w METAL HALIDE I 11-1.

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INVENTOR MICHAEL TURKAT United States Patent i 3,294,880 CONTINUOUSME'EHQD OF MANUFACTURING ABLATIVE AND REFRAETORY MATERIALS MichaelTurlrat, Bayside, N.Y., assignor, by mesne assignments, to Space AgeMaterials Corp, Woodside, N.Y., a

corporation of Delaware Filed Apr. 21, 1964, Ser. No. 361,521 6 Claims.(Cl. 26429) The present application is a continuation-in-part ofapplicants co-pending US. patent application, Serial No. 130,153, filedAugust 8, 1961 and entitled High Purity and Non-melting AblativeFilaments; applicants co-pending US. patent application, Serial No.143,634, filed October 9, 1961, and entitled Apparatus and ContinuousMethod of Manufacturing Ablative and Refractory Metal Filaments; andapplicants co-pending US. patent application, Serial No. 361,492 filedApril 21, 1964, and entitled Method of Making High Purity andNon-Melting Filaments; and applicants co-pending US. patent application,Serial No. 361,480, filed April 21, 1964 and entitled l-Iigh Purity andNon-Melting Filaments.

This invention relates to filaments and, more particularly, to anapparatus and method of manufacturing ablative and refractory filaments.

An object of the present invention is to manufacture high temperatureresistant, high strength filaments in lengths of 1 to 1000 feet or morefrom refractory or ablative materials by means of a continuous processin a high vacuum furnace.

Another object of the invention is to manufacture refractory or ablativefilaments of varied shapes and crosssections by a continuous process incontradistinction to a batch process.

An object of the invention is a continuous method of manufacturingrefractory and ablative materials by means of a rotating mandrel in ahigh vacuum furnace to provide unlimited filament lengths of controlledthickness and uniformity.

A feature of the invention is a filament formed of the class of ablativematerials including pyrolytic graphite, carbides, and combinations ofthese with refractory metals and alloys thereof, in continuous lengthsby a continuously operating process in a high vacuum furnace.

Another feature of the invention is the fabrication of high puritynon-melting crystalline filaments of ablative materials by the processof cracking or decomposing suitable gases or mixtures of gases underextremely high temperatures in a high vacuum furnace, and depositing thesame on a continually rotating mandrel or wheel.

Another feature of the invention is the fabrication of high purity,non-melting, non-porous refractory filaments of appreciable length bythe process of cracking or decomposing suitable gases or mixtures ofgases under extremely high temperatures and depositing carbon andcarbides on continually rotating mandrels having multi-.

shaped grooves therein.

In accordance with the invention, high temperature, high strengthablative refractory materials such as pyrolytic graphite by hydrocarbongas cracking techniques, or for example, to provide by metallic vapordecomposition pure crystalline refractory metals, carbides, silicidesand borides, in a variety of shapes, cross-sections and coatings by acontinuous process involving a rotating mandrel with threads andfilament lifters for scooping up the fila ments from the mandrel duringits rotation.

A variety of filament shapes and cross-sections are fabricated therebyfrom ablative refractory materials con- 3,294,889 Patented Dec. 27, 1966tinually deposited on the rotating mandrel or wheel in a continuousprocess. The resulting filaments are characterized by high purity,unlimited lengths, controlled uniform thickness, non-porosity,crystallinity and operability at superhigh temperatures in the rangefrom 5000 to 10,000" P.

For example, starting with a hydrocarbon gas such as methane,predetermined amounts of refractory metal halide vapors can be mixedtherewith, along with hydrogen carrier gas, in a vacuum furnace toproduce a composite material of pyrolytic graphite with refractory metalcarbide. An alternative procedure would end with a mixture of refractorymetal halide and hydrogen, yielding a coating of pure metal. Furtherheat treatment would yield an adherent coating by diffusion bonding tothe graphite composite substrate through the formation of anintermediate carbide layer.

The various materials provided in accordance with the invention havespecial properties, among which are that they will not melt at superhightemperatures in the range of 5000-7000" Fahrenheit, that heat isdissipated therefrom primarily by radiation and by evaporation ofmaterial through sublimation.

Pyrolytic carbon and refractory metal carbides with their high stren that superhigh temperatures, can be used in combination with a ceramic orglass filament for high strength at low temperatures and provides anideal high strength, light weight missile component.

The materials provided in accordance with the invention have propertiesand characteristics suitable for application to missile cones, rocketnozzles, missile body sections, extremely high temperature furnacelinings and for high temperature piping, filament wound containers forsolid fuel in missiles and the like.

Other objects and features will become apparent to those skilled in theart when the following disclosure is read in connection with theaccompanying drawings, wherein:

FIGURE 1 is an elevation-a1 View partially broken away of a hightemperature furnace and a stationery threaded mandrel therein.

FIGURE 1A is a perspective view of the threaded mandrel shown in FIGURE1.

FIGURE 1B shows an elevational view of a modified mandrel having theform of a flat surface or disc with spiral grooves machined therein.

FIGURE 1C is a side View of the disc mandrel shown in FIGURE 1B.

FiGURE 2 is an elevati-onal view of a modification of a high vacuumfurnace with a continuously rotating mandrel therein in accordance withthe invention.

FIGURE 3 is a front View of the rotatable mandrel illustrated in FIGURE2 showing a variety of shaped grooves therein.

FIGURE 3A shows cross-sections of varied shaped filaments derived fromthe rotatable mandrel illustrated in FIGURE 3.

FIGURE 4 is an elevational view of a filament lifter or scooper utilizedin conjunction with the rotating mandrel of FIGURE 3.

Referring to FIGURE 1, a hydrocarbon gas, such as methane, propane,benzene, butane, acetylene, ethane or toluene and hydrogen are mixedwith a metered amount of refractory metal halide in a high vacuumfurnace 20. The furnace 2%, which is water cooled has its inner walls 21coated with or insulated with ceramic material. It is electricallyheated by a graphite resistance element 22 to a high temperature,sufiicient to crack metallic and/or carbon vapors for deposition in thethreads 27 of the mandrel base.

As the decomposed gases and vapors are deposited on the stationarymandrel 26, the helical threads thereof are built up and filled withablative or refractory deposits, until a smooth, uniform coating overthe entire mandrel 26 is produced.

After a smooth coating has been laid down in the threads 27 of themandrel 26, the vacuum furnace 20 is form of mandrel is shown, wherein aflat disc 7 is pro vided with a spiral groove 8 machined in its bottomsurface, starting from the center of the disc and continuously expandingin diameter until it reaches the outer edge. The size of the flat disc 7can be varied as desired, namely, its external optimal diameter beinglimited only by the size of the furnace 20. With the disc mandrel 7, asimpler furnace feed is feasible, and a more uniform deposition ofablative materials and coating of the mandrel for forming the filament,is provided. The filaments of ablative materials can be removed from thedisc 7 by a suitable machining tool 9.

Pure crystalline filaments of materials formed by the process describedin connection with FIGURES 1, 1B, as well as filaments formed from acombination of pure refractory metals, pyrolytic graphite, refractorymetal carbides or silica, may be manufactured in accordance withtheaforementioned processes for depositing ablative materials frommetallic vapors and hydrocarbon gases cracked in high temperature vacuumfurnaces. The length, diameter, shape and combination of refractory andablative materials may be proportioned in accordance with a particularuse desired and may encompass coiled lengths of a thousand feet or more,although the various filaments per se, or combined with various b ndersas described herein may be utilized for spiral winding to form rocketbody structures as well as various intricate shapes capable ofwithstanding very high temperatures and pressures.

The data for an actual run, in thi pure pyrolytic graphite filaments, 18following charts:

Chart I shows filament density as a function of deposition temperaturewherein, the chamber pressure was 4 mm. Hg and the gas flow which wasadjusted to mamtain this pressure was 6 l.p.m. (liters per minute). Thehydrocarbon source gas used was chemically pure methane.

s case to produce illustrated by the Chart II shows the deposition rate,of the pyrolytic graphite filaments, as a function of depositiontemperature; the chamber pressure being 4 mm. Hg and the gas flow being6 l.p.m. The hydrocarbon source gas used was chemically pure methane.

4 Chart 1] Deposition rate (mils/ hour): Temperature, C. 10 1900Although hydrocarbon gas dilution with hydrogen or argon can be used, aspreviously described, the preferred method is to use only chemicallypure hydrocarbon gases.

When it is desired to produce a filament containing refractory metals,metallic vapor is introduced into the process as hereinbefore described.The proportion of metallic vapor to hydrocarbon gas can be varied from 0to 10 or more; the more parts of metallic vapor employed, the moreclosely the filament will approach that of a pure refractory metal. Theamount of hydrogen gas used can be varied from zero to one part and thepressure can be varied from 2 nun-10 mm. Hg. The preferred relationshipof the gases used can be expressed as follows:

Parts Metallic vapor 010 Hydrocarbon 1 Hydrogen 0-1 Utilizing theforegoing ablative filament manufacturing processes, various types ofrefractory and refractory alloy filament combinations can be produced.For example, a pyrolytic carbon filament can be made incorporating boronor other refractory materials such as tungsten, tantalum, niobium,molybdenum, zirconium, vanadium, titanium, thorium and chromium. Themetals are obtained by vaporizing various decomposable compoundscontaining said metals; for example, halides, oxides and variousorgano-metallic materials, such as carbonyls and dicumene compounds.Typical of refractory alloy filament combinations would be,tantalum-niobium, tita- Ilium-tantalum and molybdenum-tungsten.

A pyrolytic carbon filament incorporating boron or other refractorymaterials offers the characteristic properties of higher strength at lowtemperatures, as well as at high temperatures. For example, additions ofboron in the vapor phase during the deposition process in thefabrication of bulk pyrolytic carbon will increase the room temperaturetensile strength of this material from 18,000 p.s.i. to 30,000 p.s.i. Inthe deposition process, various metal and known metal combinations maybe produced, such as boron carbide, niobium carbide, tantalum carbide,tungsten carbide, and the like.

Referring to :the schematic diagram of FIGURE 2, a high vacuum furnace31 corresponding to the furnace shown in FIGURE 1 is similarly providedwith an inlet source 32 of methane, hydrogen and metal halide. Thesegases in various combinations are heated to a high temperaturesuflicient to crack the various gas vapors. At such high temperatures,the cracked gases and decomposition products provide a variety ofcontrollable media in the cracking area 33, from which novel refractorymetals and ablative filament materials will deposit therefrom on acontinuously rotatingmandrel 34. The rotating mandrel 34 is providedwith a variety of grooves of difierent shapes cut thereinto (likethreads) as illustrated in FIGURE 3. The deposited filaments willcorrespond in shape and cross-section with the contours of the groovesin the rotating mandrel 34, coated by refractory metal and ablativematerial deposited thereon from the original decomposition productscontaining metallic and/ or carbon vapors.

As the mandrel 34 rotates and the grooves thereof are filled withfilamentary material, a filament lifter 35 engages that fiat surface ofthe mandrel 34. The fiat lifter 35 lifts off or shaves away thefilaments from the surface coating on the mandrel 34. Peeled, fiatfilaments 38 come off the mandrel 34 as it rotates under the lifter 35.Further along in the rotation of the mandrel 34, as illustrated inFIGURE 2, groove lifters 37 operate on the mandrel by means of fingers37, have varying shapes conforming to the shapes of the grooves 36illustrated in FIGURE 3. The filament lifters 37 ride within the grooves36 and in turn lift out the filaments, which continue to pass down andaway from the rotating mandrel 34 to settle on the bottom of the furnace31.

Thereby a continuous process of forming ablative and refractory metalfilaments is provided by the rotating mandrel 34 in contradistinction tothe batch process characteristic of the stationary mandrels 26 and 7shown in FIGURES l and 1C respectively.

Pyrolytic graphite, carbide, refractory or carbide refractory alloyfilaments are feasible with this continuous rotating method ofmanufacturing ablative filaments. These basic ablative type filamentscan be later processed by various means of bonding in order to makestructures useful in missile applications and the like. Basic filamentsin continuous long lengths, in accordance with the present invention,can be protectively coated with ceramics, silicides or refractory metalsby means of a flame spray technique. Such filaments can be subjected tothe flame spray because of their superhigh temperature resistanceproperties. The basic ablative materials contemplated or provided hereinwill not melt at 5000 F. and higher and can thus be subjected to themost severe environmental high temperatures for preprocessing thefilamentary materials for subsequent production techniques. Uniformcoatings of the aforementioned protective materials in extremely longfilamentary lengths are made feasible in the aforementioned processes.

With respect to the arc type flame spray technique, it should beunderstood that gases under high pressure are ignited in a spray gun todrive metal, glass, plastics or ceramics fed into the gun in powderedform. The high pressure flame from the gun immediately melts thesepowdered materials and spurts them out in a manner similar to an airspray gun. In the persent utilization of the arc flame technique, thebasic ablative materials coated have to be able to withstand the heatand pressure developed in the spray gun, as well as to offer excellentbonding properties for the desired coating.

In order to coat carbides, it is desirable to have a metallic bondingagent within the carbide that will bind to the arc flame sprayed metal.Fine filaments of carbide can be controlled so as to have the bondingmaterials formed therewithin. The aforementioned vapor depositiontechnique may also be utilized to deposit a metal coating externallyaround the carbide filaments, which will permit the arc flame sprayingof metals and refractories thereon, thereby resulting in a stronger andmore positive bond throughout the filament structure.

For example, tantalum carbide filaments can be manufactured with atantalum vapor coating deposited thereon. This filament in turn can bewound onto a spool as in the filament wire technique of applicantscopending ap plication Serial N0. 130,153, filed August 8, 1961, and canthen have an overall spray of tantalum, providing a uniform bondedcoating between filaments and layers of filaments. In this connection, astructure of carbide within, and tantalum without, would result. Such acombination of carbide, tantalum layer laminate has the desirableproperty of offering a high stress to weight ratio as compared to solidtantalum. In missile design where weight is of extreme importance, sucha material, is most desirable inasmuch as it is able to withstandextreme temperatures beyond SO00 F., superhigh pressure and heat, but isextremely light in weight. The value of such a material can beappreciated when it is realized that enormous quantities of fuel can besaved in the operation of missiles. A similar arc flame sprayingtechnique can be still further applied in similar respects utilizingceramics as the overall coating or silica glass formed as an outer shellor surface of the laminate structure.

Various carbide refractory alloys and refractory materials can be thuscombined in various proportions and structures to permit superior bodystructures for applications to fields requiring extreme ranges ofphysical and thermal properties and specifications.

It should be apparent to those skilled in the art that variousmodifications may be made in the process and methods disclosed herein orin the resultant products thereof without departing from the spirit andscope of the invention.

What is claimed is:

, 1. A method of forming continuous lengths of a pure crystallinefilament of pyrolytic graphite, pyrolytic carbides and combinationsthereof, comprising the steps of cracking hydrocarbon gases in a vacuumfurnace at temperatures in the range of about 190023 00 C., depositingthe decomposition products thereof on a rotating mandrel having filamentpeeling means in engagement therewith and continuously peeling saiddecomposition products from said rotating mandrel in the form of acontinuous filament said mandrel having helical grooves formed thereon.

2. A method of forming continuous lengths of a pure crystalline filamentof refractory metals and alloys, and combinations thereof with pyrolyticgraphite and pyrolytic carbides, comprising the steps of crackinghydrocarbon gas and decomposable metallic compounds in a vacuum furnaceat temperatures in the range of about 19002300 C., depositing thedecomposition products thereof on a rotating mandrel having filamentpeeling means in engagement therewith and continuously peeling saiddecomposition products from said rotating mandrel in the form of acontinuous filament said mandrel having helical grooves formed thereon.

3. A method of forming continuous lengths of a pure crystalline filamentof pyrolytic graphite, pyrolytic carbides and combinations thereof,comprising the steps of cracking hydrocarbon gases in a vacuum furnaceat temperatures in the range of about 1900-2300 C., depositing thedecomposition products thereof on a rotating mandrel having a helicalgroove formed therein and further having peeling means disposed withinsaid groove, thereby forming a continuous coating of said decompositionproducts on said mandrel, removing, by cutting means, so much of saidcoating as was deposited outside of said helical groove, thereby leavinga helical filament of said coating material on said mandrel, and finallypeeling said coating material from said groove, by said peeling means,in the form of a continuous filament.

4. A method of forming continuous lengths of a pure crystalline filamentof refractory metals and alloys, and combinations thereof with pyrolyticgraphite and pyrolytic carbides, comprising the steps of crackinghydrocarbon gas and decomposable metallic compounds in a vacuum furnaceat temperatures in the range of about l900-2300 C., depositing thedecomposition products thereof on a rotating mandrel having a helicalgroove formed therein and further having peeling means disposed withinsaid groove, thereby forming a continuous coating of said decompositionproducts on said mandrel, removing, by cutting means, so much of saidcoating as was deposited outside of said helical groove, thereby leavinga helical filament of said coating material on said mandrel, and finallypeeling said coating material from said groove, by said peeling means,in the form of a continuous filament.

5. A method of forming continuous lengths of a pure crystalline filamentof pyrolytic graphite, pyrolytic carbides and combinations thereof,comprising the steps of cracking hydrocarbon gases in a vacuum furnaceat temperatures in the range of about 1900-2300 C., depositing thedecomposition products thereof on a rotating mandrel having a spiralgroove formed therein and further having peeling means disposed withinsaid groove, thereby forming a continuous coating of said decompositionproducts on said mandrel, removing by cutting means, so much of saidcoating as was deposited outside of said spiral groove, thereby leavinga spiral filament of said material on said mandrel, and finally peelingsaid coating material from said groove, by said peeling means, in theform of a continuous filament.

6. A method of forming continuous lengths of a pure crystalline filamentof refractory metals and alloys, and combinations thereof with pyrolyticgraphite and pyrolytic carbides, comprising the steps of crackinghydrocarbon gas and decomposable metallic compounds in a vacuum furnaceat temperatures in the range of about 1900-2300 C., depositing thedecomposition products thereof on a rotating mandrel having a spiralgroove formed therein and further having peeling means disposed withinsaid groove, thereby forming a continuous coating of said decompositionproducts on said mandrel, removing, by cutting means, so much of saidcoating as was deposited outside of said spiral groove, thereby leavinga spiral filament of said material on said mandrel, and finally peelingsaid coating material from said groove, by said peeling means, in theform of a continuous filament.

' 8 References Cited by the Examiner UNITED STATES PATENTS.

1,960,215 5/1934 Ellis et al. 264309 XR 2,304,206 12/1942 Reichel264-215 XR 2,532,295 12/1950 Gardner 23,208 2,796,331 6/1957 Kaufiman eta1. 23-209.2 XR 2,862,748 12/1958 Bailey et al 1218 XR 2,957,756 10/1960Bacon 23209.3 XR 2,990,601 7/1961 Wagner 264309 XR 3,138,434 6/1964Diefendorf 23-2093 XR FOREIGN PATENTS 1,249,305 11/ 1960 France.

693,937 7/1940 Germany.

274,883 8/ 1928 Great Britain.

OTHER REFERENCES Metal Industry, Aug. 13, 1954, Metal Carbides (Carter),pp. 123125, London Periodical, copy available in 23-208 A.

ROBERT F. WHITE, Primary Examiner.

ALEXANDER H. BRODMERKEL, Examiner.

J. A. FINLAYSON, Assistant Examiner.

1. A METHOD OF FORMING CONTINUOUS LENGTHS OF A PURE CRYSTALLINE FILAMENTOF PYROLYTIC GRAPHITE, PYROLYTIC CARBIDES AND COMBINATIONS THEREOF,COMPRISING THE STEPS OF CRACKING HYDROCARBON GASES IN A VACUUM FURNACEAT TEMPERATURES IN THE RANGE OF ABOUT 1900*-2300*C., DEPOSITING THEDECOMPOSITION PRODUCTS THEREOF ON A ROTATING MANDREL HAVING FILAMENTPEELING MEANS IN ENGAGEMENT THEREWITH AND CONTINUOUSLY PEELING SAIDDECOMPOSITION PRODUCTS FROM SAID ROTATING MANDREL IN THE FORM OF ACONTINUOUS FILAMENT SAID MANDREL HAVING HELICAL GROOVES FORMED THEREON.